Method and apparatus for controlling fuel injection timing in a compression ignition engine

ABSTRACT

The method and apparatus for generating start of combustion signals associated with the combustion events in a diesel engine (10), and for using such signals to control the timing of fuel delivery to the engine. The combustion event is sensed, as by an electrostatic (230, 330) or optical (130, 430) sensor, and signal conditioning circuitry (32) provides a start-of-combustion (SOC) signal (34) which is directly and precisely indicative of the time of the onset of combustion. The sensors (130, 230) include self-cleaning capabilities (48, 248) for extended operating life on an engine. The sensors may be incorporated in the structure of a glow plug (330, 430). The SOC signal (34) is advantageously supplied to a timing control circuit (26) which delivers a timing control signal (28) to a fuel delivery device, such as the controller (16&#39;) associated with a fuel pump (16). The control circuit (26) stores (65) one or more start of combustion values (SOC*) which indicate the desired timing, relative to an engine cycle (24), for the start of the combustion event as a function of speed (25) and load (27). One or more adjustment signals (ΔSOC) are stored (75) and applied (67, 68) as a function of speed and load to adjust the desired signal (SOC*) such that the control signal (28, SOC c ) is corrected for delays. The actual SOC signal (34) is compared (71) with the desired signal (66) to generate an error signal (72) which may be used to finely adjust the stored (75) ΔSOC signal for particular speed and load conditions.

This is a continuation of co-pending application Ser. No. 791,891, filedJan. 14, 1985, now abandoned, which is a continuation of applicationSer. No. 532,293, filed Sept. 14, 1983, now abandoned, which is acontinuation of application Ser. No. 286,130, filed July 23, 1981, nowabandoned.

TECHNICAL FIELD

This invention relates to the control of fuel injection timing incompression ignition engines and more particularly to the control ofsuch fuel injection timing based on the measured timing of the onset ofcombustion. The invention additionally relates to the development oftiming signals which are accurately and directly representative of theonset of combustion in a combustion chamber of the engine.

BACKGROUND ART

Continuing requirements to achieve improved fuel efficiency and reducedexhaust gas emissions of compression ignition engines, hereinafterreferred to as diesel engines, has stimulated the development ofelectronically controlled fueling systems offering the potential forproviding more precise engine control. The gains achievable in dieselengine performance through the introduction of electronic fuel controlsdepend to a great extent on the control strategy implemented, theaccuracy to which specific engine operating parameters can be measuredand controlled and the ability to maintain such control throughout theoperational life of the engine.

In compression ignition engines, one of the most critical operatingparameters is fuel injection timing. Presently, control of the time ofinjection is determined mechanically and/or hydraulically. The timingfunction has typically relied only upon measurements of mechanicaltiming points, such as crank angle, flywheel position, piston positionand/or injector actuation to provide the requisite timing control. Whilesuch control was historically effected mechanically and/orelectromechanically, recent developments have placed increasing emphasison the utilization of electronics. Representative of these timingtechniques and implementations are U.S. Pat. Nos. 4,033,310 and4,265,200 which sense injector actuation to provide corrective feedbackinformation to electronic controls which determine and control thetiming of fuel delivery, or injection, by fuel delivery apparatus.

Those systems, however, fail to provide for the fact that in dieselengines, unlike spark ignition engines, the start of combustion withinthe cylinder does not directly relate under most circumstances to themechanical timing point, such as injector actuation. Engine operatingconditions such as cylinder wall temperature, air inlet temperature,engine load and speed and fuel quality all influence the specific pointor time in the engine cycle at which combustion takes place within thecylinder. An additional complication is the contemplated introduction ofa broad spectrum of new fuels, fuel blends (i.e. alcohol and wateremulsions), and synthetic fuels widely ranging in cetane rating. Thesefactors combine to introduce a variable delay between the time of fuelinjection and the start of combustion which may typically be 5°-20° ofcrank angle. To accommodate such variations in the onset of combustionintroduced by the above factors, the purely mechanical timing systemmust be augmented with precise information on the aforementioned engineoperating parameters, as well as with a direct measurement of fuelquality (cetane rating) and fuel density. From this information, it thenbecomes possible to estimate the instant at which combustion begins.Obviously, the complexity of this approach along with the large numberof required sensor inputs limits accuracy and practicability.Furthermore, this approach can, at best, provide only an estimate of theonset of combustion and cannot provide compensation for enginevariables.

While the introduction of electronic control systems to diesel enginesis relatively new, considerable development has occurred with sparkignition gasoline engines. Specifically, efforts have been made toimprove spark ignition engine performance via the electronic controlsassociated with engines. For instance, in U.S. Pat. No. 4,181,944, whichin turn refers to a different Japanese patent application KoKai(laid-open) No. 4903/72, there is a general discussion of usingcombustion pressure sensors for monitoring the pressure in one or moreengine cylinders and for modifying a previously-stored spark ignitiontiming scheme if the sensed pressure indicates deterioration of thecylinder pressure. Mention is also made of sensing the ion current inthe spark plugs in lieu of a pressure measurement. These techniques,however, are intended for use with spark ignition engines and do notsense the timing of the combustion event, but rather its quality.

Various techniques other than an analysis of pressure have also existedfor indicating some combustion-related characteristics of an engine. Twosuch examples, U.S. Pat. Nos. 2,523,017 and 4,232,545, utilize an ioniccurrent detector to detect knocking or "detonation" in a spark ignitedengine, either for analytical or corrective control purposes. U.S. Pat.No. 3,051,035 describes an optical combustion monitoring device fordetecting a flame-out condition in aircraft jet engines. However, thesepatents are not concerned with the timing of the onset of combustion norwith the development of a timing signal for a diesel engine, norspecifically with control of fuel injection timing based on a directmeasurement of the onset of combustion.

Accordingly, it is a principal object of the present invention toprovide improved control of the timing of fuel delivery in dieselengines. Included within this object is the provision of a method andapparatus for controlling such fuel delivery in an accurate and precisemanner as a function of the onset of combustion in the engine.

It is a further object of the invention to provide apparatus foraccurately sensing the onset of combustion and generating correspondingstart-of-combustion timing signals therefrom. Included within thisobject is the provision of such apparatus which is relatively durableand long lived, yet relatively inexpensive.

In accordance with one aspect of the invention, there is provided themethod of and apparatus for controlling fuel delivery in a compressionignition engine at least partly as a function of the onset of combustionin the engine. Command signals indicative of the desiredstart-of-combustion timing are provided as a function of engineoperating parameters and are utilized in open-loop manner to control thetiming of fuel delivery. The command signals are modified or trimmed asnecessary to correct for the variable delays which generally occurbetween the time (i.e. engine crank angle) of the fuel delivery and thestart of combustion. The appropriate correction of those control signalsis achieved by detecting the actual instant of the start-of-combustionin a respective combustion chamber, comparing that actual time (i.e.crank angle) with the time which was desired, thereby to detect anyerror, and correcting the original control signal by an amount equal toor proportional to the error. The desired start of combustion values maybe previously determined and stored for a full range of engine speedsand loads. The correction signals may also be stored as a function ofengine speeds and loads and may be periodically updated by thedetermined error values. The processing of error values is done in amanner providing dynamic and accurate correction for the control signaleven though non-monitored engine operating conditions may change.Provision is made for a cold-starting advance.

In accordance with another aspect of the invention, a signal generatoris provided for responding to a direct property of the combustionoccurring in a cylinder to generate a timing signal indicative of theonset of combustion. A sensor in communication with a cylindercombustion chamber detects the particular property of combustion beingmonitored, the level of that detected property normally changing at arapid rate, typically increasing, at the onset of combustion. The sensedproperty is then converted, as by signal conditioning means, to anelectrical timing signal which accurately indicates the onset ofcombustion.

In one embodiment, the sensor is optical in character and senseselectromagnetic radiation, i.e. light of some frequency or frequencyrange, emitted by the combustion event. A photodiode provides anelectrical analog of the sensed light. Signal conditioning circuitrythen squares the leading edge of the electrical analog, which leadingedge then is indicative of the onset of combustion and is used incontrolling the timing of fuel delivery in the diesel engine. Thecombustion radiation may be sensed by a heat-resistant optical elementand coupled, as by a fiber optical cable, to the photodiode.

In another embodiment of the invention, the sensor detects the level ofionization in the combustion chamber. An electrical current is developedand, following the type of signal conditioning described in thepreceding paragraph, provides an electrical signal accurately indicativeof the onset of combustion. The sensor includes one or more electrodesmounted in a ceramic insulator.

For certain engines, either type of sensor may assume the general formof a glow plug for mounting in the precombustion chamber of the engine.A heating element may be included in the gross sensor structure.

The start of combustion signal generator is employed in combination withthe fuel delivery control system of the engine throughout operation ofthe system to provide dynamic control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the diesel engine fuel controlsystem including the signal generator for indicating the start ofcombustion;

FIG. 2 is a functional block diagram of the timing control circuitry ofthe fuel control system of FIG. 1;

FIG. 3 is a diagrammatic sectional view illustrating the sensor of thestart of combustion indicating signal generator positioned in operativerelation with a combustion chamber of the diesel engine;

FIG. 4 illustrates one embodiment of a start-of-combustion signalgenerator;

FIG. 5 illustrates an embodiment of an electrostatic start-of-combustionsignal generator;

FIG. 6 illustrates a modified embodiment of the FIG. 5 signal generatorwith the sensor combined with a glow plug and positioned in aprechamber; and

FIG. 7 illustrates a portion of a modified embodiment of the FIG. 4signal generator in which the sensor is combined with a glow plug.

BEST MODE FOR CARRYING OUT THE INVENTION

The onset of combustion in the cylinder of a diesel engine isaccompanied by a rapid change in several phenomena within or near thecombustion chamber, including a pressure rise, the production of chargedparticles, the emission of photons, a rise in temperature, an increasein the acoustic noise level and the like. On an experimental basis, asin a laboratory, the pressure rise can be employed to determine thepoint in the engine cycle at which combustion commences. However, thelarge change in pressure produced by the compression stroke may to someextent mask the change in pressure resulting from the combustionprocess. Additionally, pressure transducers having sufficient lifeexpectancy for mass-market utilization on diesel engines are relativelyexpensive at present for that particular application. Furthermore,engine designers in an effort to reduce diesel engine noise areattempting to minimize in more modern engine designs the rate ofpressure rise produced by the combustion process. Accordingly, at leastat present, some of the other mentioned physical phenomena appear topresent equal or better opportunity for detecting the onset ofcombustion. Those phenomena should, and generally do, exhibit a rapidand substantial level change at the onset of combustion. By using one ormore of such phenomena, a signal herein designated "start of combustion"can be obtained and developed, which signal is indicative of the actualbeginning of combustion in the combustion chamber. Typically, thissignal determines the start of combustion to an accuracy of less thanone engine crank angle degree.

Two such phenomena accompanying the onset of combustion and serving toillustrate the principles of the invention are the production ofsignificant levels of excitation and ionization. The excitationmanifests itself in the emission of electromagnetic radiation, such aslight. Direct measurements of either the emitted light or ionizationlevels resulting from the in-cylinder combustion process have been foundto provide highly accurate and repeatable indications of the onset ofcombustion within the cylinder. Furthermore, the output signal levelsfrom either optical or electrostatic detectors have been found to bemore than adequate for measurement purposes under a wide range of engineoperating conditions.

Referring to FIG. 1, there is diagrammatically illustrated amulticylinder internal combustion engine 10 of the compression ignition,or diesel, type. Fuel is delivered in a predetermined sequence to therespective combustion chambers 12 of the respective cylinders 14 by afuel delivery system including fuel delivery apparatus 16 and suitableinjectors 18. The fuel is injected into the respective combustionchambers 12 by means of the injectors 18. As used herein, the term"combustion chamber" is intended to also include the prechamber on somediesel engines where combustion "first" begins, such engines being ofthe "indirect" injection type.

Some cyclically moving portion of engine 10, as for instance flywheel20, is monitored, as by engine timing transducer 22, to provide periodicsignals indicative of the position of certain parts of the engine. Morespecifically, transducer 22 generates a pulse each time a reference mark23 on flywheel 20 passes. The reference mark typically indicates somecrank angle, as for instance zero, when one specific piston is at aknown position such as its top dead center position, and provision maybe made for responding only to top-dead center indications at thecompletion of a respective compression stroke. Moreover, that enginetiming signal might be generated at a predetermined angle, e.g. 120°before top dead center. It will be appreciated that some other movingcomponent of the engine or fuel pump might be monitored to provide theengine timing signal 24 provided by transducer 22. Engine timing signal24 is a principal input signal to on-board control circuitry 26 whichprovides a timing control signal 28 to the fuel delivery apparatus 16 aswill be described. Control circuitry 26 also receives other inputsrepresentative of other engine operating conditions as derived fromsuitable sensors of known design, such as input 25 representative ofengine speed and input 27 representative of engine load (i.e. throttlerack position). The fuel delivery apparatus 16 is also responsive tofuel quantity control signals (not shown) to deliver a controlledquantity of fuel. The fuel quantity control signals are functions offoot pedal position and engine governor characteristics, and theirdevelopment can be provided mechanically or electronically in a knownmanner not forming part of the present invention.

Fuel delivery apparatus 16 may typically be a diesel fuel injectionpump, such as the Model 100 injection pump manufactured by AmericanBosch and disclosed in U.S. Pat. No. 3,726,608, capable of delivering apressurized charge of fuel to each of the injectors 18 at theappropriate time and in sequence for injection into the respectivecombustion chambers 12. The fuel pump is mechanically driven by theengine and derives its basic, or reference, timing in that manner.However, the timing of the delivery of those fuel charges to and throughthe injectors and into the combustion chamber 12 may be varied byadvancing or retarding the timing cam of the fuel pump in response toengine operating parameter of speed and load.

The advance/retard timing mechanism of the fuel delivery apparatustypically comprises a piston and cylinder arrangement in whichdisplacement of the piston acts either directly or indirectly toazimuthally rotate a ring on which one or more timing cams ispositioned. The displacement of the piston may be done hydraulically, inthe general manner of U.S. Pat. Nos. 4,265,200 and 4,033,310. Some typeof actuator 16', as for instance a stepper motor, a torque motor or thelike, responds to control signal 28 from control circuit 26 forcontrolling the advance/retard mechanism.

Finally, if the fuel injectors are of the solenoid-actuated type, fueldelivery timing is done directly at the injector solenoid in response tocontrol signal 28 which then must be expressed and utilized as a timesignal, relative to some crank angle, rather than a cam angledisplacement signal. In such instance, the injector solenoid isanalogous to controller 16' insofar as it effects the desired timing offuel delivery.

In accordance with the invention, a further signal is provided inaddition to engine timing signal 24, engine speed signal 25 and engineload signal 27, which is indicative of the response of a specificcylinder 14 to the injection of fuel. More particularly, one or moresensors 30 responsive to some sensible phenomenon coincident with andchanging sufficiently rapidly to be accurately indicative of the onsetof combustion in respective combustion chambers 12, for instance, theelectromagnetic radiation or the ionization accompanying the onset ofcombustion, operate in conjunction with signal developing circuitry 32to provide respective start-of-combustion (hereinafter referred to asSOC) timing signals 34.

SOC timing signal 34 is applied as an input to control circuitry 26 forprecisely and accurately indicating the instant of the actual onset ofcombustion within a respective combustion chamber 12 for successivecombustion cycles of the respective cylinder 14. The sensor 30 providesSOC timing signals 34 to on-board control circuitry 26 throughout theoperation of engine 10 in a vehicle and is thus able to provide acontinuous dynamic control function. The SOC timing signal 34 isutilized for the development of an error signal which may then be usedin various ways, depending upon the control strategy of control circuit26, to provide and/or modify dynamically the fuel delivery timingcontrol signal 28.

The aforementioned U.S. Pat. No. 4,265,200, incorporated herein byreference, discloses one possible configuration for the present controlcircuitry broadly represented by block 26 in FIG. 1 herein, subject tothe following modifications. Firstly, and most importantly, the engineperformance curves stored in memory are predicated on the desired timing(i.e. angle) of the start of combustion as a function of engineoperating conditions. Correspondingly, the parameter sensed and fed backfor comparison is the timing of the start of combustion, i.e. thepresent SOC signal 34, rather than an indication of the start ofinjection. Additionally, because the combustion event in a cylinder isstatistical in nature, suitable numerical processing is preferablyemployed to derive a timing signal. This can be accomplished directly byemploying, for example, a first order numerical filter or by utilizing arunning numerical average of the SOC signal. Also appropriate signalprocessing is employed to accommodate the situation when no combustionoccurs in cylinder, as experienced when operating a vehicle with aclosed fuel rack.

The aforementioned U.S. Pat. No. 4,033,310, incorporated herein byreference, discloses another possible configuration for the presentcontrol circuitry of block 26, subject to the following modifications.The generated signal which is proportional to engine speed and loadwould in the present instance represent the desired timing of the startof combustion and the sensed parameter for error signal generation wouldnow be the start of combustion rather than the injector-actuation. Theresultant signal will control the actuator motor to effect a pump timingwhich satisfies the desired start of combustion characteristics. As inthe above paragraph, suitable means for filtering or averaging the SOCsignal or the error signal would normally be provided.

Each of the aforedescribed control circuits, while being generallysuitable for the implementation of the present invention, possessescertain limitations. For instance, in U.S. Pat. No. 4,265,200, thecoarse control signal is supplied hydraulically and is a function ofengine speed only, and only a trim signal is provided via theclosed-loop circuitry illustrated. That trim control is inherently slowin its response in order to avoid instability. In U.S. Pat. No.4,033,310, the pump timing is provided as a function of multiple engineoperating conditions, thereby enabling the timing actuator motor to morerapidly respond to changes in multiple engine operating conditions.However, the correction signal which is added to the basic command orcontrol signal is a proportional value of the error such that the errorcan never go to zero so long as any correction is needed. In eithercase, because the correction value is developed only as a function ofthe error resulting during the immediately past operating cycle, it maynot adequately correct during intervals of rapidly changing operatingcondition if the correction actually required differs at differentoperating conditions.

In accordance with an aspect of the invention, a preferred arrangementof control circuitry 26 is diagrammatically depicted in functional formin FIG. 2. Control circuitry 26 typically comprises a microprocessor ormicrocomputer, or a portion thereof, suitably programmed in a knownmanner for performance in accordance with the following functionaldescription. It will be understood that appropriate digital-to-analogand analog-to-digital circuitry (not shown) is included to convert thesignals from one form to the other. A number of digital words, forinstance possibly 64 or 256, defining an optimized map of desiredcombustion angle (or time) settings as functions of engine speed (S) andload (L) are stored, as in an addressable ROM 65. These combustion anglesettings are typically determined empirically by mapping a particularclass of engine and fuel system, and reflect the timing of combustionwhich will provide desired fuel economy and reduction of exhaustemissions. The engine mapping is conducted using the particularstart-of-combustion phenomenon to be sensed by sensors 30 in order toprevent any time disparities that may exist between two different typesof start-of-combustion phenomena. These desired combustion anglesettings are designated SOC* in the map stored in ROM 65 as depicted inFIG. 2. These SOC* settings identify the desired instant when combustionis to begin in a particular combustion chamber, and are expressed eitheras a time, or preferably an engine crank angle, relative to somereference. The reference is typically that of an engine part, normallythe top dead center (TDC) position of a piston in the relevant cylinder.The mechanical linkage of the engine and fuel delivery apparatus 16 aretypically set, as by a keying arrangement or the like, at the time ofproduction and assembly such that fuel delivery at a normal position orstatus of the advance/retard mechanism coincides with fuel delivery ator near TDC, or possibly at some other fixed angular bias of the engine.

Because a significant delay exists from the time of fuel pump ejectionuntil the actual start of combustion, typically due to various hydraulicand compression ignition delays, a second set or map of engine crankangle values is stored in additional ROM 90 and is designated ΔSOC_(r)as depicted in FIG. 2. The ΔSOC_(r) values may be established fromengine mapping as a function of engine load and speed and will typicallycontain values which correspond either with some suitable nominalspeed-load function for such engines or with a speed-load function whichis predetermined to approximately correct or compensate each of the SOC*values for the predetermined or pre-estimated delays between pumpactuation and the start of combustion. While respective SOC* valuesmight be modified by the appropriate summation with correspondingΔSOC_(r) values, variations of as much as 10°-15° in the actual onset ofcombustion may occur due to changes in temperature, fuel quality,humidity and the like. Therefore, in accordance with the invention,provision is made for changing the ΔSOC_(r) signal in a dynamic fashionto reflect such variations in the delay as determined from a directmeasurement of the combustion event.

In functional operation of the preferred system, the ΔSOC_(r) map storedin ROM 90 is transferred to an addressable random access memory (RAM) 75at each engine start-up, as represented by transfer control circuit 93.Then, during operation of the timing control system, the data stored inRAM 75 generally designated ΔSOC and initially comprising only ΔSOC_(r)values, is appropriately summed at junction 68 with corresponding SOC*data from ROM 65 as a function of then-existing engine speed and loadconditions to provide a corrected time control signal SOC_(c), alsoidentified as signal 28, to actuate stepper motor 16' controlling thetiming of fuel injection.

Upon the injection of fuel and its subsequent combustion within acombustion chamber of engine 10, a SOC timing signal 34 from sensor 30and signal conditioning circuitry 32 is generated. SOC signal 34 isprecisely indicative of the instant, and thus impliedly the angle, atwhich combustion starts. The SOC signal 34 then comprises an input tocircuit 26 to provide feedback data of the response of engine 10 to thetiming of the fuel delivery. Assuming the SOC* signal 66 and thecorrected timing control signal 28 represent angular values, the SOCtiming control signal 34 is converted from a pure time indication to oneof angle, represented by the measured SOC_(m) signal 70. The conversionis provided by appropriate circuitry 69, possibly also comprising partof a suitably programmed microprocessor, which considers the timing ofSOC signal 34 relative to a reference event such as the TDC timeindicated by signal 24 and in view of the speed of the engine indicatedby signal 25.

The SOC_(m) signal 70 is then compared with the desired SOC* signal 66to obtain an error signal SOC_(e) identified by reference numeral 72.The comparison is represented at and by the summation junction 71, andthe error signal SOC_(e) represents the magnitude and sense of theerror. In the event no SOC signal 34 is provided to circuit 26 withinsome predetermined monitoring interval in each operating cycle, eitherbecause of sensor failure or because the fuel rack is closed at no load,the conversion circuitry 69 and summing junction 71 are conditioned tofunction such that the value of error signal SOC_(e) is zero. The loadsignal 27 is additionally provided as an input to circuit 69, whichcircuit is additionally conditioned to provide a separate output signal69' which may be provided to an annunciator if no SOC signal 34 occursand the load signal 27 is not zero, thereby indicating failure of theSOC sensor.

Depending upon the duration of a SOC* signal on lead 66 to comparingjunction 71, it may be desirable to include a suitable form of delay, asrepresented by dotted block 85, to ensure that the SOC* signal appearsat junction 71 when the naturally delayed SOC_(m) signal 70 for thatparticular SOC* signal also appears thereat. This need is particularlyemphasized during rapidly changing operating conditions of amulticylinder engine when it is desired to compare the SOC_(m) signalwith the precise SOC* signal which was responsible for that SOC_(m)response.

The error signal SOC_(e) is then utilized, either directly or preferablyas some numerically filtered or time-averaged quantity, to modify theΔSOC angle value then stored in RAM 75 for the speed and load conditionswhich produced the error. The modification of the stored ΔSOC signal issuch as to reduce the error the next time those particular speed andload conditions occur, assuming no further changes arise in theoperating parameters. In the event no SOC signal 34 occurs, due tosensor 30 failure, the input of a zero SOC_(e) value to modify the ΔSOCalready stored in RAM 75 simply means that no update of that data willbe made. However, it will be appreciated that the ΔSOC data alreadystored in RAM 75, or possibly a reload therein of ΔSOC_(r), willnormally be sufficient in combination with the SOC* data to provide afail-soft fully operational capability.

During operation of the engine, the ΔSOC map in RAM 75 is modified orupdated by replacing a ΔSOC data word stored for a particular speed andload condition with a new data word for those same conditions in theevent the error signal SOC_(e) has a value other than zero.Alternatively, in its simplist configuration, a single correctionindependent of speed and load may be utilized to correct the ΔSOC mapwhen a non-zero error signal SOC_(e) occurs. In the preferredarrangement, that modification of the stored ΔSOC value as a function ofthe error developed for the same speed and load conditions is madeutilizing a numerical filter represented by block 80, which minimizesthe effect of the small but finite statistical variation associated withthe actual combustion event. The numerical filter 80 may be included ina known manner as part of the program for a microprocessor. The value ofΔSOC to be newly stored in RAM 75, i.e. ΔSOC_(n), equals the presentlystored value of ΔSOC, i.e. ΔSOC_(p), and the value of the instant errorsignal SOC_(e) divided by some numerical constant M, i.e. ΔSOC_(n)=ΔSOC_(p) -SOC_(e) /M. The value of M will be dictated by the combustionstatistics associated with a certain engine design. In practice, it hasbeen found that a value in the range of approximately 3-8 is suitable toprovide a sufficiently rapid update of engine operating conditions whilemaintaining a high degree of precision.

Tests of the SOC sensor 30 on various automotive diesel engines haverevealed that the SOC signal 34 provides a timing signal accuracy ofbetter than ±1.5° with an 80% reliability, based on "long term"operation of approximately 2000 revolutions of the engine. Viewed inanother manner, in a test in which a series of 26 samples each comprisedof a small number (i.e. 2-4) of consecutive combustion events wasanalyzed, it was determined that the arithmetic average for each andevery sample was within ±1° of a "most probable" SOC angle determined bya long-term average.

In view of the foregoing discussion, it will be understood that thecorrection ΔSOC map in RAM 75 is automatically and quickly adjusted as afunction of individual engine speed and load operating points to provideΔSOC signals 67 which are used in conjunction with the SOC* signal 66 toprovide SOC_(c) signal 28. Assuming the ΔSOC values stored in RAM 75 arepositive values representative of the crank angle delay between fuelpump actuation and start of combustion, then the negative sign atsumming junction 68 associated with ΔSOC lead 67 signifies that the pumpactuation timing must be advanced relative to SOC* signal 66 to providecombustion at the desired crank angle, SOC*.

During cranking or start-up of a diesel engine when the combustionchambers are relatively cold, i.e. at ambient air temperature, it isnecessary to advance the timing of fuel delivery as a function of thattemperature and relative to the combined value stored in the SOC* ROM 65and the ΔSOC RAM 75 for those speed and load conditions to initiatecombustion and complete start-up. For instance, in one automotive dieselengine, the amount of such advance additionally required may be in therange of 8° to 15° of crank angle for temperatures ranging from 30° C.down to -10° C. respectively.

Therefore, in the illustrated embodiment, to provide the indicatedtiming of fuel delivery via SOC_(c) signal 28 during cold start-up, afurther signal 91, additionally designated ΔT_(c), is selectivelyextended to junction 68 for summing with the SOC* and ΔSOC signals, ifdeemed necessary. The ΔT_(c) signal 91 is representative of theadditional angle by which the fuel delivery should be advanced, asrepresented by the negative sign, at a certain temperature ortemperature range of the air, the engine block or, preferably, the fuel.A function generator 92 receives the temperature signal T as an inputand provides an appropriate output signal ΔT_(c). In extreme examples,the function generator 92 might generate only a single value for ΔT_(c)for all fuel temperatures T, or it may generate a large number of valueseach corresponding with a respective different fuel temperature T. In apreferred arrangement, only a limited number of ΔT_(c) values aregenerated, each associated with a respective range of fuel temperaturesT.

A gating circuit 94 having the ΔT_(c) signal as an input from functiongenerator 92 may be controlled by a gating signal 96 to extend theΔT_(c) signal to junction 68 only during cranking conditions. The gatecontrol signal 96 is provided by the circuitry 69, or an adjunctthereto, such that gate 94 is enabled to pass the ΔT_(c) signal onlyduring engine cranking when no SOC signal is sensed from the engine.After a sufficient number of compression cycles have occurred to warmthe engine and fuel to a level at which combustion begins and SOCsignals are generated, the gate may be disabled and the ΔT_(c)correction removed from the SOC_(c) signal 28. It will be recalled thatwhile no SOC signals are generated, the SOC_(e) error signal has a valueof zero. Once the SOC signals begin and the ΔT_(c) correction signal isremoved, and before the engine is fully warmed to normal operatingtemperature, the SOC_(e) signal may have a relatively large value. Thesevalues of SOC_(e), somewhat moderated by numerical filter 80, serve tomodify the ΔSOC values in RAM to permit continued warm-up. As anoptional alternative, gate 94 might be omitted and the signal T_(c)decreased as a function of increasing temperature, with the adaptivecapability of RAM 75 aiding in this regard.

While the described SOC_(c) timing signal 28 is representative of anengine crank angle, and thus also a pump cam angle, to which the timingof actuation of the fuel delivery apparatus 16 should be advanced orretarded and may be analog or digital in form, depending upon the typeof signal required to effect control of the controller 16', that signalmight alternatively be representative of a time in the engine cycle atwhich a solenoid-actuated injector is to be actuated to inject fuel intothe engine. In this latter instance, the signal would time the injectoropening, and the subsequent delay until the onset of combustion would besomewhat less than from pump actuation, but the general control conceptwould be the same.

One major advantage of the present invention is that the need fortime-consuming and often complex adjustment of the mechanicalinterrelationship of the fuel pump and the engine at the time ofassembly to then attain precise timing is generally obviated. Instead,by establishing a mechanical relationship between the engine and pumpwhich is approximately as desired, as by the aforementioned keying or asimilarly simple referencing technique, the open-loop timing commandobtained from ROM 65 and RAM 75 is sufficient to provide at leastfunctional timing commands and the further adaptive provision formodifying or correcting the ΔSOC data in RAM 75 ultimately corrects forany inaccuracies or errors contained in the set-up timing.

An optional further feature is a provision for periodically returningthe corrected ΔSOC map stored in RAM 75 to memory 90 for use as the ΔSOCreference at the next engine start-up, assuming RAM 75 is of thevolatile type in which its contents are lost when power is removed. Insuch instance, memory 90 would be of the programmable type, such as anEEPROM, and the map from RAM 75 would be entered in it periodicallyand/or during some brief interval in which power is maintained atshutdown. This capability would insure that upon successive enginestart-ups the timing system would immediately include all correctionspreviously made to the very first ΔSOC_(r) map after it was entered inRAM 75, rather than requiring those corrections be made again byoperation of the engine following each start-up.

Referring to FIG. 3, there is illustrated one general form of the SOCsensor, here designated 130, positioned in operative relationship withthe combustion chamber 12 of cylinder 14. A piston 15 is illustrated incylinder 14 near the TDC position at the moment combustion beginsfollowing injection of fuel by injector 18. The combustion process isaccompanied by the emission of electromagnetic radiation, such asphotons 17, and by ionization of the air/fuel mixture, represented byelectrical charges 19. The sensor 130 of FIG. 3 is optical in nature anddetects the electromagnetic radiation or emission of photons 17coincident with combustion. Sensor 130 is mounted in the head 21 ofengine 10 such that it is in optical communication with thelight-emitting combustion process in combustion chamber 12.

Referring to FIG. 4, the optical SOC sensor 130 is illustrated ingreater detail in combination with its signal developing andconditioning circuitry 32 utilized to generate the start of combustiontiming signal 34. The optical sensor 130 includes an optical element,such as a quartz or sapphire rod 40 which acts as a viewing windowhaving a proximal end suitably embedded in a metal mounting plug 42which is adapted to be threadably inserted into the head 21 of engine10. Optical element 40 is bonded by means of a high-temperature cementor is brazed to plug 42 to provide a high temperature, high pressure,gas-tight seal. Optical coupling is provided between the mounted end ofoptical rod 40 and a suitable transducer, such as photodiode 44.Photodiode 44 also forms part of sensor 130 and converts the sensedelectromagnetic radiation or light into an electrical signal. Thephotodiode 44 may either be directly housed in or mounted on plug 42 orpreferaby, is spaced therefrom to minimize the adverse effects of heatand is optically coupled with element 40 by means of a fiber optic cable46. The facing end portion of fiber optic cable 46 is retained in acentral bore in mounting plug 42 in close facing relationship withoptical rod 40 by suitable means not specifically illustrated, such as acollar clamp. A dust cover, such as a protective boot, may supplementthe mounting of fiber optic cable 46 to mounting nut 42. The oppositeend of fiber cable 46 is mounted and maintained in fixed operativerelation with photodiode 44 in a suitable manner which insures goodoptical coupling.

The formation and/or accumulation of soot or carbon on the front face ofoptical rod 40 is substantially eliminated and the rod is physicallyprotected by locating the distal end of that rod within acircumferential gas plenum 48 formed with plug 42 and by maintainingthat end of the rod at an elevated temperature. The plenum 48 surroundsthe optical rod 40 along its distal end. The diameter of the plenumadjacent the distal end of rod 40 gradually decreases to form a narrowannular orifice 50 between the plug 42 and the extreme distal end of rod40 to increase the gas velocity and thus the cleansing action in thatregion. The gases within cylinder 14 and combustion chamber 12 arecompressed into the plenum 48 during the compression stroke and rapidlyexit therefrom through the orifice 50 during the power stroke, therebyaiding in the desired cleansing of the optical rod 40. The rod 40 is ofa material which is a poor thermal conductor and extends about onecentimeter or more from its point of mounting contact with plug 42 tomaintain its distal end, during engine operation, at a temperaturesufficiently high to impede the accumulation of occluding deposits byinhibiting condensation and by producing dry carbonized material whichis easily removed by the high velocity gas flow from the plenum. Thetemperature at the distal end of rod 40 is typically about 425° C.

Referring to the signal-developing circuitry 32, the light whichaccompanies combustion within chamber 12 and which is sensed by rod 40and is converted by photodetector 44 to an electrical signal isrepresented by the current waveform 52 which comprises an electricalanalog of the intensity of the light detected. The signal 52 comprisesthe input to circuitry 32. It will be noted that the signal 52, as afunction of time, exhibits a very rapid increase at the onset ofcombustion. The time of this increase is designated T_(SOC) herein. Themagnitude of the signal may continue to increase thereafter, but at aslower rate, and then diminishes as the excitation accompanyingcombustion diminishes. The current signal 52 is passed through acurrent-to-voltage converter 54 which provides the output signal voltagehaving the waveform 56. The converter 54 is provided with sufficientgain to drive it into saturation and thereby provide the resultingwaveform 56 with a particularly steep wave front at time T_(SOC). Theamplitude of signal 56 at time T_(SOC) is relatively large and thatsignal is then extended to an input of comparator 58 having a muchsmaller reference voltage 60 applied to its other input. When the signal56 exceeds the reference voltage 60 at time T_(SOC), the comparator 58provides an output signal 34 having a squared, substantially verticalwave front at time T_(SOC) which is utilized as the start of combustion(SOC) timing signal. It will be appreciated that additional circuitry(not shown) may be utilized if it is wished to convert the leading edgeof the waveform 34 at time T_(SOC) to a single spike rather than theleading edge of a square wave pulse. In either event, the very shortrise time of the signal at time T_(SOC) provides a precise signal foraccurately identifying the onset of combustion in a combustion chamberand is utilized as the SOC timing signal 34 provided to control circuit26.

Alternate forms of a SOC sensor which rely on the detection of theionization resulting from combustion of the air/fuel mixture aredepicted in FIGS. 5 and 6. FIG. 5 depicts a basic form of ionization orelectrostatic type SOC sensor, here designated 230. The combustion offuel within diesel engine 10 results in the rapid formation of ions inthe combustion chamber and/or the precombustion chamber during fuelcombustion. A rapid increase in the level of ionic charges occurs at theinstant combustion begins. The electrostatic sensor 230 is intended tosense this rapid increase in the ionization level and convert it to anelectrical SOC timing signal 34.

A center electrode 240 is mounted in a suitable metallic mounting plug242 via the intermediate supporting and electrically insulatingstructure of ceramic insulator 241. The electrode 240, insulator 241 andmounting plug 242 are hermetically bonded to one another, as with asuitable heat resistant cement, or are brazed to insure the pressureintegrity within the combustion chamber. The mounting plug 242 of FIG. 5may be threaded into a threaded opening through the head of engine 10 toplace it in communication with the respective combustion chamber 12. Theinnermost end of electrode 240 may be substantially flush with the innerend of plug 242 and preferably is relatively short such that it remainsrelatively cool to avoid the emission of electrons. The center electrode240 is spaced from the inner circumference of the mounting nut 242 suchthat an annular or circumferential plenum 248 is formed therebetween.The insulator 241 includes a tapered surface for increasing the lengthof that surface between the plug 242 and the center electrode 240 tominimize electrical leakage. The tapered insulator 241 and the plenum248 introduce certain turbulences to the gases entering that area topromote the avoidance or elimination of soot formation on the electrode240 and the surface of the insulator.

The plug 242 is in direct electrical connection with the engine 10,typically at ground potential. A source 245 of a small finite DCvoltage, i.e. 5 volts, is applied to the electrode 240 via an electricalconnecting cable 246 for facilitating the establishment of an electricalcurrent flow through the electrode and the cable as a result of theionic charges developed by combustion in the combustion chamber 12. Thedirection of current flow is a function of the polarity of the appliedvoltage. The developed current is proportional to the level ofionization in the combustion chamber which in turn reflects the level ofactivity in the combustion process. That electrical current, appearingin conductor 246, is applied as the input to signal developing circuitry32 constituted in substantially the same manner as hereinbeforedescribed.

Since operation of the electrostatic sensor 230 is predicated onelectrical charges from the combustion process arriving at electrode240, the precise location of this sensor within the combustion chamberis important. Specifically, combustion takes place more nearly in thecenter of the chamber in a region which varies in size in relation tothe engine operating speed and load conditions. Accordingly, the timingand the intensity of the ionization signal sensed by sensor 230 isdependent upon its positioning in the chamber relative to the origin ofthe combustion process. In view of this consideration and because theremay be little or no additional room available in the head of certaindiesel engines for the installation of additional structural elements,the SOC sensor may be incorporated with other functional engineelements.

Accordingly, referring to FIG. 6, there is illustrated yet anotherembodiment of the electrostatic SOC sensor, here designated 330. In thisembodiment, the SOC sensor 330 takes the shape of a conventional glowplug heater normally inserted in the prechamber 12' associated with manydiesel engines. In certain instances, the SOC sensor and glow plugheater may be combined in a single structural element. The prechamber12' is typically mounted above and communicates with the main combustionchamber 12 via an orifice 11. The fuel injector nozzle 18' is mounted soas to inject fuel into the prechamber 12' where it undergoes preliminarycombustion and is expelled via orifice 11 to the main combustion chamber12 for the completion of combustion. Typically, glow plugs are mountedin each of the prechambers 12' to facilitate ignition of the fuel in theprechamber, particularly during start-up and especially cold weatherstart-up. The structural configuration and positioning of the glow plugstructure within prechamber 12' relative to the fuel injection path isknown to be critical and has been optimized by various enginemanufacturers. Accordingly, that portion of SOC sensor 330 which extendswithin prechamber 12' has been configured and dimensioned externally andpositioned to conform as nearly as possible to the configuration andpositioning of that portion of a conventional glow plug normallyinserted into such prechamber.

The electrostatic SOC sensor 330 operatively positioned in prechamber12' in FIG. 6 is comprised in the main of a metal mounting plug 342, anionization sensing electrode 340 and an insulator 341 which ispositioned between and electrically isolates the electrode 340 from themounting plug 342 and thus from the engine 10. The mounting plug 342 isconveniently threaded into the threaded opening in the wall of aprechamber 12' which normally receives a glow plug. The mounting plug342 typically includes an axial bore therethrough for housing certainelectrical elements to be hereinafter described. The longitudinallyinner, or distal, end of plug 342 includes an annular seat in which ispositioned an annular ceramic insulator 341 hermetically sealed theretoby a suitable heat resistant cement. An annular recess in thelongitudinally inner, or distal, wall of the insulator 341 provides aseat for the proximal end of the electrode 340 which is hermeticallysealed thereto by a suitable heat resistant cement. The electrode 340 isprovided with a surface geometry and configuration which closelyconforms to that of the glow plug heater designed for utilization in theparticular prechamber 12'. Typically, the electrode 340 is a tubularmetal shell having a blind, or closed, distal end and being open at itsproximal end which is in seated engagement with insulator 341.

To provide the requisites of an ionization sensor, it is only necessarythat an electrical conductor 346 be connected at one end to theelectrode 340 and that its other end be led out through the bore in plug342 to signal conditioning circuitry, as for instance circuit 32illustrated in FIG. 4. Additionally, a source of signal developingvoltage analogous to source 245 in FIG. 5 may be connected to the lead346.

The structure comprising electrostatic SOC sensor 330 in FIG. 6 mayinclude additional elements to enable it to operate cooperatively oralternatively as a glow plug for the purpose of facilitating fuelcombustion in the prechamber 12' during cold start-up conditions. Forinstance, the SOC sensor 330 may include an elongated rigid spar 352mounted thereto and extending coaxially within the central bore in amanner analogous to a conventional glow plug. The spar 352 may be ofheat resistant material and is preferably an electrical insulator, asfor instance a ceramic. A wire-like heating element 350 is wound aboutthe distal end of spar 352 which is positioned within the recess formedby electrode 340. One end of heater wire 350 is placed in electricalconnection with the engine 10, as by connection with conductive ring 354seated in electrical contact with plug 342. The other end of heater wire350 may be led out through the rear of the sensor structure forselective connection to a source of electrical power, as for instancethe 12 volt supply of an automobile. The proper placement of insulatingsupports and/or insulating coatings on the respective conductors 346 and350 insure their electrical isolation from one another and from certainelements of the sensor structure.

The optical SOC sensor 130 described with reference to FIGS. 3 and 4 mayalso be structured similar to the external structure of theelectrostatic SOC sensor 330 of FIG. 6 to provide a sensor configurationwhich conforms externally to that of a conventional glow plug forintroduction to the prechamber 12'. Moreover, the optical SOC sensor mayinclude a heating element to function as a glow plug. Specificallyreferring to FIG. 7, a portion of an optical SOC sensor 430 isillustrated in which the base plug or mounting structure includes atubular extension 442' having an external geometry which substantiallyconforms to that of a conventional glow plug and to the electrode 340 ofthe electrostatic SOC sensor 330 of FIG. 6. The optical element 440 isgenerally longer than its counterpart illustrated in FIG. 4, and asuitable heating element 449 is concentrically disposed about theelement 440 within plug extension 442' for providing heat duringstart-up. An aperture 451 in the distal end of extension 442' is inoptical registry with the distal end of optical element 440 to providethe necessary optical path to the combustion site. The aperture 451 issized and positioned relative to the distal end of the optical element440 to form a narrow annular orifice 450 therabout for the high speedentry and exhaust of gases to and from the plenum 448 for cleaning theoptical element.

It will also be understood that a multicylinder diesel engine may beprovided with SOC sensors in one, all, or less than all, of thecombustion and/or precombustion chambers of the engine in developing therequisite timing control signals. The utilization of more than one SOCsensor not only improves the precision of timing control, but also mayprovide engine diagnostic information. If the engine includesprecombustion chambers, each precombustion chamber may be equipped witha SOC sensor having the dual capabilities of generating a signalindicative of the start of combustion and providing heat to facilitatethe combustion of fuel in the prechamber during start-up. Alternatively,one prechamber may be provided with a SOC sensor capable only ofproviding a SOC timing signal and the remaining prechambers wouldinclude conventional glow plugs having no SOC sensing capability.Moreover, the SOC sensor might instead be incorporated in the structureof the injector so as to minimize the number of penetrations of thecombustion chamber wall, this being of particular value in directinjection engines which do not have a precombustion chamber and a glowplug entry.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention. Itwill be appreciated that the invention described herein provides animproved fuel delivery timing control for diesel engines and can beimplemented on a fully electronic fueling control or in conjunction witha mechanical or hydraulic-mechanical governor control without departingfrom the spirit of the invention. Moreover, although detaileddiscussions of an optical and an electrostatic SOC sensor exist herein,it will be appreciated that SOC sensors which respond to other SOCphenomena are within the ambit of the invention. For instance,rapid-response temperature sensor, or similarly rapid sound and/orpressure transducers, or the like might also be used.

We claim:
 1. A system for controlling the timing of injection of dieselfuel into a combustion chamber of a diesel engine,comprising:light-transmissive means having a light-input portionconfronting the interior of the part of said combustion chamber in whichinitial combustion of said fuel normally takes place, to receive andtransmit light produced by said combustion in said chamber;photoresponsive means supplied with light from said light transmissivemeans and responsive thereto to produce a substantially instantaneousincrease in its electrical output upon the start of said combustion;signal shaping means responsive to said electrical output of saidphotoresponsive means for producing a start-of-combustion signalsubstantially simultaneously with said substantially instantaneouslyincrease in said electrical output; electrical control means responsiveto said start of combustion signal for controlling said timing ofinjection of said diesel fuel; and means supporting said light inputportion of said light transmissive means in a position where it isexposed to said light produced in said combustion chamber, saidsupporting means providing a high enough temperature and a great enoughrate of combustion gas flow across said light input portion to effectself-cleaning of it.
 2. A fuel timing system for a compression ignitionengine, said system including:means for delivering fuel to said enginefor combustion, said fuel delivery means being responsive to a timingcontrol signal for controlling the timing of fuel delivery by said fueldelivery means; a first signal generator comprising means for sensing aphenomenon in a combustion chamber of said engine which is directlyrepresentative of the onset of combustion therein and providing arepresentative signal thereof, said sensed combustion property being oneof optical electromagnetic radiation or ions, emitted by the combustion,and means for conditioning asid representative signal to provide anelectrical signal precisely indicative of the actual instant of theonset of combustion, said sensing means being structured to provideself-cleaning thereof during and substantially only as a directconsequence of operation in a said combustion chamber to facilitatecontinuous operation, said self-cleaning occurring substantiallyindependently of external engery; second signal generating means forproviding an electrical signal indicative of engine timing; third signalgenerating means for providing an electrical signal indicative of enginespeed; fourth signal generating means for providing an electrical signalindicative of engine load; control circuit means operatively connectedwith and being responsive to each of said onset of combustion signal,said engine timing signal, said engine speed signal and said engine loadsignal for providing said timing control signal, said control circuitmeans including means for providing a signal representative of a desiredtiming of the onset of combustion as a function of said engine speed andsaid engine load and further means responsive to said desired timing ofonset of combustion signal and to said actual instant of onset ofcombustion signal each referenced to said engine timing signal, foradaptively providing said timing control signal such that the subsequentactual start of combustion substantially coincides with the timing ofsaid desired start of combustion; wherein said engine is constructed tomount a conventional glow plug heater extending through an opening in awall thereof into a portion of the combustion chamber, that portion of asaid conventional glow plug heater positioned within said chamber havinga characteristic external structure and said combustion sensing meansbeing externally structured for mounting in said engine in substantiallyidentical substitution for said external structure of said conventionalheater otherwise positioned within said chamber; and wherein thestructure of said combustion sensing means additionally includes heatingmeans to retain the heating function of the replaced conventionalheater.
 3. A signal generator for use with a compression ignition engineto provide electrical signals directly and precisely indicative of theinstant of the onset of combustion, said signal generatorcomprising:means adapted to be mounted in operative communication with acombustion chamber of said compression ignition engine to sense a directproperty of the combustion process within said combustion chamber andprovide an electrical signal representative thereof, said sensedcombustion property being one of ions or optical electromagneticradiation, emitted by the combustion, said sensing means beingstructured to be substantially self-cleaning during and substantiallyonly as a direct consequence of said operative communication with a saidcombustion chamber and substantially independently of external energy,whereby substantially continuous operation with a said combustionchamber is afforded; amplification means responsive to said electricalsignal indicative of the combustion process for substantially increasingthe magnitude of at least the leading edge of said signal indicative ofthe combustion process; and threshold means responsive to saidmagnitude-increased signal exceeding a predetermined relatively-lowmagnitude threshold level for providing an electrical output signalhaving a leading edge which is substantially vertical relative to thetime base of interest in a compression ignition engine, said signalleading edge being precisely indicative of the instant of actual onsetof combustion; wherein said sensing means includes a structure having anelongated tubular outer surface along that portion thereof suited formounting within the prechamber of a diesel engine, said surface geometrysubstantially conforming to that of a conventional glow plug heaternormally positioned within such prechamber; and wherein said sensingmeans structure additionally includes heating means to include thefunction of a glow plug heater.
 4. A fuel timing system for acompression ignition engine, said system including:means for deliveringfuel to said engine for combustion, said fuel delivery means beingresponsive to a timing control signal for controlling the timing of fueldelivery by said fuel delivery means; a first signal generatorcomprising means for sensing a phenomenon in a combustion chamber ofsaid engine which is directly representative of the inset of combustiontherein and providing a representative signal thereof, said sensedcombustion property being one of optical electromagnetic radiation orions, emitted by the combustion, and means for conditioning saidrepresentative signal to provide an electrical signal preciselyindicative of the actual instant of the inset of combustion, saidsensing means being structured to provide self-cleaning thereof duringand substantially only as a direct consequence of operation in a saidcombustion chamber to facilitate continuous operation, saidself-cleaning occuring substantially independently of external energy;second signal generating means for providing an electrical signalindicative of engine timing; third signal generating means for providingan electrical signal indicative of engine speed; fourth signalgenerating means for providing and electrical signal indicative ofengine load; control circuit means operatively connected with and beingresponsive to each of said onset of combustion signal, said enginetiming signal, said engine speed signal and said engine load signal forproviding said timing control signal, said control circuit meansincluding means for providing a signal representative of a desiredtiming of the onset of combustion as a function of said engine speed andsaid engine load and further means responsive to said desired timing ofonset of combustion signal and to said actual instant of onset ofcombustion signal each referenced to said engine timing signal, foradaptively providing said timing control signal such that the subsequentactual start of combustion substantially coincides with the timing ofsaid desired start of combustion; wherein said sensed phenomenon isoptical electromagnetic radiation emitted by the combustion process;wherein said sensing means comprises a heat resistant optical elementadapted for mounting through a wall of said engine combustion chamber;wherein said sensing means further includes a photodetector, saidphotodetector being spaced a significant distance from said opticalelement and being optically coupled therewith by a fiber optic cable;wherein said means for conditioning said representative signal toprovide an electrical signal precisely indicative of the actual interestof the onset of combustion comprises: amplification means responsive tosaid electrical signal indicative of the combustion process forsubstantially increasing the magnitude of at least the leading edge ofsaid signal indicative of the combustion process; and threshold meansrepsonsive to said magnitude-increased signal exceeding a predeterminedrelatively-low magnitude threshold level for providing an electricaloutput signal having a leading edge which is substantially verticalrelative to the time base of interest in a compression ignition engine,said signal leading edge being precisely indicative of the instant ofactual onset of combustion.
 5. The system of claim 1, comprising aplenum chamber partially surrounding said light-transmissive meansadjacent said light input portion thereof, said plenum chamber having anopening to said combustion chamber through which said light inputportion views the interior of said combustion chamber, said plenumchamber having a cross-sectional area adjacent said light input portionwhich decreases in the direction toward said combustion chamber, therebyto increase the velocity and self-cleaning action of the combustiongases at said light input portion.
 6. The system of claim 5, whereinsaid light-transmissive means is a light-conductive rod, and said lightinput portion comprises an end region of said rod.
 7. The system ofclaim 5, wherein said signal-shaping means comprises means foramplifying said electrical output of said photoresponsive means, andmeans for producing a start of combustion signal by detecting the timeat which said amplified output reaches a predetermined threshold level.